Today's progress... 3D Bezier F-curves are now editable in the viewport for unconstrained child bones with inherited rotation and asynchronous/independent curves! I learnt a lot from studying Crouch's script which has a larger but different feature set and currently works with objects not bones (mine currently works with bones and not objects). Hopefully my script shown below, will help push the discussion along and go some way towards bringing this feature to blender in a finished state before it hits maya!
The script is available here but be warned its in heavy beta, so back up your animation first! Feel free to bug report in the comments below. I've coded an on screen help (which will start when you enter the 3D f-curve edit mode) as the shortcuts had to be unusual to save messing with the keymaps.
There's extensive discussion of the autodesk technology preview which sparked all of this here (though its not really a new technology at all as apparently DigitalFish Reflex had it a few years back).
In other news an animator whose work I've been following recently is Dustin Grella. If your mind is buzzing as much as mine with all that discussion on 3D fcurves you'll probably find it refreshingly low tech... here's Bag for a Banana Peel.